The monitoring of high voltage electrical switchyards for revenue metering, instrumentation control, bus and line protection are generally carried out using current transformers. The current transformers are electrically connected to the high voltage conductors and therefore, are themselves high voltage devices which can and do develop faults resulting in damage to the switchyard.
Research into ways of eliminating the use of current transformers in the monitoring of high voltage currents has resulted in a number of alternatives being proposed. However, all of the proposed methods so far have the common feature requiring some form of attachment to the high voltage system being monitored. Most of the methods proposed are based on a transducer which uses the Faraday effect to monitor magnetic fields in a closed magnetic path around the conductor. However, due to the closeness of the coil to the conductor being monitored, the transducer is substantially at the same potential as the conductor.